This application is related to commonly assigned U.S. patent application Ser. No. 08/924,228, entitled "Liquid Level Sensor" as invented by Ronald W. Okoren, Ali Ameen and Matthew A. Shepeck and filed on even date hereof.
The present invention is directed to an oil flow protection system for an air conditioning or refrigeration system. The system is an active and robust system which avoids compressor failure by stopping compressor operation upon failure of the oil circulation or return system.
The present invention is discussed in terms of screw compressors for air conditioning systems, but is contemplated to apply to all compressors whatever the application. Like many other compressors, screw compressors require oil flow to the compressor so as to lubricate bearings and prevent long term degradation's of the bearings. Additionally, oil flow is needed to seal the rotors in a screw compressor to avoid reduced performance and to cool the rotors to prevent frictional heating.
Oil flow is needed by a compressor to lubricate the bearings and enhance their life. Additionally, in screw and scroll compressors, oil is used to seal the rotors, the absence of such a seal resulting in reduced compressor performance. Also, the lubrication of rotors can prevent frictional heating while cooling the rotors, and can prevent the radial growth and interference of rotors with adjacent compressor components. If the oil circulation system fails and compressor operation is allowed to continue, compressor failure and damage will ultimately result.
U.S. Pat. Nos. 5,431,025 and 5,347,825, both to Oltman et al., are directed to an oil charge loss protection arrangement for a compressor. Essentially both patents disclose comparing the temperature of a liquid in the oil system with the temperature of saturated refrigerant, and generating a signal to shutdown the compressor when the comparison indicates that the differential is off range. These patents are commonly assigned with the present invention and are incorporated herein by reference.
An oil protection system is desired which proves that there is oil in the compressor or that there is an immediately available supply of oil trapped in lines feeding the compressor prior to any starting of the compressor. Additionally, a perfect oil protection system would prove flow in the oil line during compressor operation and prove that the flow is a liquid rather than a vapor or at least is a liquid foam. Additionally, the desired oil protection system should prove that the flow is high in oil quantity (i.e., less than 30% refrigerant by weight).